It is common industry knowledge that the rotating barrel of an axial multiple piston fluid translating unit tends to move or tilt relative to a porting plate or a porting surface of the housing thereof. Such movement or tilting results from the pistons operating against an inclined cam plate as well as radial force components resulting from the pistons being in different planes.
Tilting of the barrel causes the barrel face to be inclined relative to the porting surface. This can result in undesirable fluid leakage and localized contact between the mating surfaces with resultant damage thereto.
These problems have been recognized in the prior art, and numerous solutions proposed therefor. Once such proposed solution is disclosed in U.S. Pat. No. 3,808,950. This patent discloses a pump barrel having a port plate rotatable therewith against a valve plate with a sleeve extending into counterbores in both the barrel and the port plate and a separate O-ring seal associated with each end of the sleeve and its respective counterbore. This system also includes separate washers disposed at each end of the sleeve in the respective counterbores to compress the O-ring seals and provide an axial thrust force urging the port plate into contact with the valve plate. This results in an unnecessarily complicated and expensive design requiring the providing of recesses at each end of the sleeve to receive the O-rings. It is also necessary to provide counterbores in both the piston barrel and the port plate rotatable therewith to receive the opposite ends of the sleeve and the seals. Additionally, it is necessary to provide washers in each of the counterbores at the opposite end of the sleeve to compress the O-rings and to provide a thrust force of the port plate against the valve plate. This system also provides undesirable stiffness in the relationship of the barrel to the port plate due to engagement of the sleeve with the counterbores in each of those elements and could result in tilting forces being transferred from the barrel to the port plate. Provision of sufficient clearance around the sleeve to avoid or minimize such tilting force transfer could result in failure of the seals due to extrusion of those seals into the annular clearance around the sleeve by the extremely high pressures encountered in a piston pump of this general type. It is therefore apparent that such a system is highly undesirable, not only from an economic standpoint but, also from the high risk that the system will not operate to provide the intended freedom and/or early failure of the system due to blowout of the seals.
U.S. Pat. No. 4,007,663 discloses another proposed solution to the problem of barrel tilting in a hydraulic translating unit. This patent teaches a system in which a flanged slipper pad includes a cylindrical end engaging each of the cylinder bores in the rotating barrel and a flanged end engaging a port plate secured to the housing or head of the pump or motor. An annular plate defines a series of openings therein telescoped over the flanged sleeves underneath said flanges and utilizes a series of springs between the annular plate and the end of the barrel for urging the flanged ends of the sleeves against the port plate for sealing purposes. Since the port plate is secured to the housing or head of the pump and the slipper pads are telescopically engaged in the outer ends of the cylinder bores in the barrel, rotation of the barrel may causes a tendency for the slipper pads to tilt in the cylinder bores which could cause leakage and undesirable contact of the slipper pads with the valve plate. This could also be further aggravated by tilting of the cylinder block. Due to the relatively lengthy engagement of the slipper pad with the cylinders, tilting of the cylinder block may cause further tilting of the slipper pads relative to the valve plate. This system is also complicated in that it involves many innerfitting small parts and therefore would be considered to be excessively expensive.
U.S. Pat. No. 4,481,867 discloses another proposed solution to the problem of the cylinder block tilting with the resultant undesirable effects. This patent teaches a seal plate disposed between the cylinder block and a valve plate for rotation with the barrel and in sliding contact with the valve plate. The plurality of cylinder bores in the cylinder block each contains a telescopically mounted bushing consisting of a thin-walled cylinder which can make tight contact with a inner wall surface of the bore as expanded in diameter by a high pressure liquid within the bore and the bushing. The other end of the bushing defines a flanged portion which is engaged against the seal plate and is urged into contact therewith by a compression coil spring and a plate positioned between the flanges of the bushings and the end surface of the cylinder block. This structure requires the provision of excessive space between the end of the barrel and the valve plate thus resulting in a larger overall unit and greater space requirements. The expansion of the bushings in the cylinder bores for sealing purposes could also severely restrict the ability of the bushings to move relative to the cylinder block thus creating undesirable motion of the bushings relative to the seal plate as the cylinder block tilts. This system would also be undesirably complicated and expensive to manufacture.
U.S. Pat. No. 4,201,117 teaches yet another proposed solution to the problem of barrel tilting relative to a porting surface within the pump or motor housing. In this system, a toroidal distributor, rotatable with the barrel, is disposed in sliding contact with a distribution flange. The toroidal distributor includes a series of spherical pockets on the side thereof facing the barrel for reception of the complimentary spherical ends of a plurality of cylindrical plugs telescopically engaging the cylinder bores in the pump barrel. The cylindrical plugs are secured to the toroidal distributor by thin-walled tubes extending through the openings therein and flanged at their opposite ends to retain the cylindrical plugs in sealing relation to the spherical surfaces of the toroidal distributor. The cylindrical plugs each define annular grooves around the outer periphery thereof for reception of sealing rings which engage the inner surface of the cylinder bores of the barrel. This system results in an undesirable length of engagement of the cylindrical plug within the cylinder bore which, unless adequate clearance is provided, may restrict motion of the barrel relative thereto, thus causing a disruption of the sealing relationship of the peripheral surfaces on the cylindrical plug and the toroidal distributor. This system is also undesirably complex and expensive to manufacture due to the various parts thereof and the required precision machining of the spherical sealing surfaces on both the cylindrical plugs and the toroidal distributor.
In view of the undesirable aspects of the above described prior art systems, it is highly desirable that means be provided for simply and effectively compensating for tipping of the barrel within an axial piston fluid translating unit without affecting or disrupting the close tolerance, running seal between the outer end of a barrel plate and the porting surface of such translating units. It is also desirable that the sealing means between the barrel and the barrel plate be axially compact to minimize the physical size of the fluid translating unit. It is also desirable that the length of the flow path from the end of the barrel to the porting plate be as short as possible to minimize the volume of fluid residing therein.
The present invention is directed to overcoming one or more of the problems as set forth above.